Ultraviolet emitting device with shaped encapsulant

ABSTRACT

Embodiments of the invention include a light emitting diode (UVLED), the UVLED including a semiconductor structure with an active layer disposed between an n-type region and a p-type region. The active layer emits UV radiation. The UVLED is disposed on a mount. A transparent encapsulant is disposed over the UVLED. The transparent encapsulant has an angled sidewall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 15/402,621,filed on Jan. 10, 2017, assigned to the present assignee andincorporated herein by reference.

BACKGROUND Description of Related Art

The bandgap of III-nitride materials, including (Al, Ga, In)—N and theiralloys, extends from the very narrow gap of InN (0.7 eV) to the verywide gap of AlN (6.2 eV), making III-nitride materials highly suitablefor optoelectronic applications such as light emitting diodes (LEDs),laser diodes, optical modulators, and detectors over a wide spectralrange extending from the near infrared to the deep ultraviolet. Visiblelight LEDs and lasers can be obtained using InGaN in the active layers,while ultraviolet LEDs (UVLEDs) and lasers require the larger bandgap ofAlGaN.

UVLEDs with emission wavelengths in the range of 230-350 nm are expectedto find a wide range of applications, most of which are based on theinteraction between UV radiation and biological material. Typicalapplications include surface sterilization, air disinfection, waterdisinfection, medical devices and biochemistry, light sources forultra-high density optical recording, white lighting, fluorescenceanalysis, sensing, and zero-emission automobiles.

The extraction efficiency from such UVLEDs is often undesirably low.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a UV-emitting device (UVLED)disposed on a mount and covered with a shaped encapsulant.

FIG. 2 is a plan view of multiple pixels in a flip chip UVLED.

FIG. 3 is a cross sectional view of one pixel in the UVLED.

FIG. 4 is a cross sectional view of a UVLED covered with a shapedencapsulant, with a reflective material disposed adjacent theencapsulant.

FIG. 5 is a cross sectional view of a UVLED covered with a shapedencapsulant.

FIG. 6 is a top view of the device of FIG. 5.

FIG. 7 is a top view of a device with features formed in the encapsulantover the UVLED.

FIG. 8 is a cross sectional view of a UVLED disposed in a reflector cupformed on a mount, and covered with a shaped encapsulant.

FIG. 9 is a cross sectional view of a UVLED covered with a shapedencapsulant and positioned in a parabolic reflector.

FIG. 10 is a cross sectional view of a UVLED covered with a shapedencapsulant with a graded index of refraction.

FIG. 11 is a photograph of a portion of a UVLED covered with a shapedencapsulant.

DETAILED DESCRIPTION

Though the devices described herein are III-nitride devices, devicesformed from other materials such as other III-V materials, II-VImaterials, Si are within the scope of embodiments of the invention. Thedevices described herein may be configured to emit visible, UV A (peakwavelength between 340 and 400 nm), UV B (peak wavelength between 290and 340 nm), or UV C (peak wavelength between 210 and 290 nm) radiation.The radiative power emitted by the UVLEDs described herein may bedescribed as “light” for economy of language.

Embodiments of the invention are directed to structures and techniquesfor increasing the extraction efficiency from UVLEDs.

FIGS. 1, 4, 5, 8, 9, and 10 are cross sectional views of UVLEDs 1attached to a mount, and covered with an encapsulant, according toembodiments of the invention. The encapsulant may be shaped, asdescribed below.

In each of FIGS. 1, 4, 5, 8, 9, and 10, the UVLED 1 is attached to amount 40. Mount 40 may be any suitable material that is highly thermallyconductive (for example, with a thermal conductivity of at least 170W/mK in some embodiments), highly electrically insulating, andmechanically rigid (for example, with a coefficient of thermal expansionthat matches or is close to that of UVLED 1). Examples of suitablematerials for mount 40 include but are not limited to ceramic, diamond,AN, beryllium oxide, silicon or electrically conductive material such assilicon, metal, alloy, Al, or Cu, provided the electrically conductivematerial is appropriately coated with an insulating layer such assilicon oxide, silicon nitride or aluminum oxide, or any other suitablematerial. In some embodiments, circuitry and/or other structures such astransient voltage suppression circuitry, driver circuitry, or any othersuitable circuitry may be disposed within mount 40, or mounted on asurface of mount 40, such that the circuitry or other structures areelectrically connected to UVLED 1, if necessary.

In each of FIGS. 1, 4, 5, 8, 9, and 10, conductive pads 42 are formed onthe top surface of the mount. UVLED 1 is electrically and physicallyconnected to mount 40 through pads 42. At least two electricallyisolated pads 42 are provided per UVLED 1, one coupled to the n-typeregion of the UVLED 1 and one coupled to the p-type region of the UVLED1. Pads 42 may be, for example, any material that is suitable forbonding UVLED 1 including, for example, gold, silver, tin-silver-copper(SAC), or gold-tin (AuSn). Pads 42 may be formed on the surface of mount40 by any suitable technique including, for example, plating.

The contacts of UVLED 1 (described below) are connected to pads 42 by aninterconnect (not shown), which may be any suitable material such as,for example, solder or gold. UVLED 1 may be connected to pads 42 by anysuitable technique including, for example, gold-gold interconnection,soldering, or flux-assisted eutectic reflow techniques.

In each of FIGS. 1, 4, 5, 8, 9, and 10, the area on the mount 40surrounding UVLED 1 may be reflective. In some embodiments, the surfaceof the mount is reflective. In some embodiments, the mount is coatedwith a reflective layer 44. Reflective layer 44 is a material that ishighly reflective to the radiative power emitted by UVLED 1. Reflectivelayer 44 may be any suitable material including, for example, a metal,aluminum, multi-layer metal stacks, alloys, a dielectric, multi-layerdielectric stacks, multi-layer metal and dielectric stacks, orreflective particles such as Polytetrafluoroethylene (PTFE, which may beknown by the trade name Teflon®) or aluminum oxide disposed in atransparent material, such as UV-resistant silicone. Reflective layer 44is at least 70% reflective of radiative power with wavelengths between250 and 350 nm in some embodiments, and at least 85% reflective ofradiative power with wavelengths between 250 and 350 nm in someembodiments.

A metal reflective layer 44 such as aluminum may be formed by, forexample, plating, electron beam deposition, or evaporation. Reflectivelayer 44 may be a metal stack. For example, one or more layers thatfacilitate adhesion of the metal reflective layer 44 to the underlyingsurface (for example, a surface of mount 40 and/or a surface of pads 42)may be formed prior to metal reflective layer 44. Examples of suchadhesion layers include nickel, titanium, or alloys thereof. One exampleof a suitable metal stack is 100 nm Ti disposed in direct contact withthe underlying surface, followed by 500 nm Al. The metal stack may beformed by any suitable technique. In one embodiment, the metal stack canbe formed by e-beam deposition, and the pattern can be formed by aphotoresist lift-off process as is known in the art.

A reflective layer 44 that is reflective particles disposed in atransparent material may be formed by, for example, dispensing, molding,stencil printing, screen printing, or any other suitable technique.Reflective particles may be Al₂O₃, polytetrafluoroethylene (PTFE), orAl, disposed in silicone or any other suitable material that is lowindex, UV-resistant, and transparent to light between for example 250 nmand 350 nm. In some embodiments, the transparent material iselectrically insulating. In some embodiments, the difference inrefractive index between the particles and the transparent materialcauses scattering of light incident on the reflective layer 44. Forexample, commercially available UV-suitable silicone (such as, forexample, Schott UV-200) may have a refractive index of no more than1.42. Al₂O₃ particles may have a refractive index of 1.8. The differencebetween 1.42 and 1.8 may cause suitable scattering. The particles may bemicron sized or nanometer sized.

Reflective layer 44 may improve extraction from the device.

In each of FIGS. 1, 4, 5, 8, 9, and 10, UVLED 1 is covered with anencapsulant 46. Encapsulant 46 may protect UVLED 1, for example frommoisture, may protect wire bonds formed to UVLED 1 (if used), forexample from breakage or failure, and may protect metal layers on oradjacent UVLED 1, for example from oxidation. Encapsulant 46 may be, forexample, UV-resistant silicone, fused silica, glass, IHU UV transmissiveglass available from Isuzu Glass, Inc., quartz, or sapphire. Dependingon the material, encapsulant 46 may be formed over UVLED 1 bydispensing, molding, spin coating, or spraying a liquid or semi-solidover the UVLED 1, then curing, or forming a pre-formed encapsulantseparate from UVLED 1, for example by molding or grinding and polishing,or by any other suitable technique. The thickness of the encapsulant,i.e. the distance between the top surface of encapsulant 46 and the topsurface of reflective layer 44 may be at least 500 μm in someembodiments, no more than 2 mm in some embodiments, at least 750 μm insome embodiments, and no more than 1 mm in some embodiments. In theexamples below, encapsulant 46 is, for example, a silicone layer.

In each of FIGS. 1, 4, 5, 8, 9, and 10, the sidewall 48 of encapsulant46 is shaped. The examples illustrated in FIGS. 1, 4, 5, 8, 9, and 10need not have shaped sidewalls in some embodiments, and in someembodiments, in a single device, only some of the sidewalls are shaped.As illustrated, the sidewall is shaped such that rather than a verticalsidewall, the sidewall slopes inward, such that the encapsulant is widerat the top surface than at the bottom surface (the bottom surface beingin contact with the top surface of the mount). Though an inward angle isillustrated, the sidewall may also angle outward from top to bottom,such that the encapsulant is wider at the bottom surface. Asillustrated, the sidewall is angled, such that the sidewall forms anacute angle with the top surface of the mount. The angle may be, forexample, at least 30° in some embodiments, at least 45° in someembodiments, no more than 60° in some embodiments, and less than 90° insome embodiments. As illustrated, the angled sidewall is flat. In someembodiments, the sidewall may be curved (convex or concave), or mayinclude a curved portion and a flat portion. In some embodiments, thesidewall has more than one profile. For example, a top section of thesidewall may be angled, and a bottom section of the sidewall may bevertical; a top section of the sidewall may be vertical, and a bottomsection of the sidewall may be angled; a top section of the sidewall maybe curved, and a bottom section of the sidewall may be vertical; a topsection of the sidewall may be vertical, and a bottom section of thesidewall may be curved; a top section of the sidewall may be angled, anda bottom section of the sidewall may be curved; or a top section of thesidewall may be curved, and a bottom section of the sidewall may beangled. Any other suitable non-vertical sidewall may be used.

In some embodiments, all, none, or a portion of the top surface ofencapsulant 46 may be textured, for example by roughening or bypatterning. The texturing may improve light extraction from theencapsulant 46. In some embodiments, the top surface of the encapsulant46 is formed into a lens or other suitable structure. In someembodiments, particles the cause scattering are mixed with theencapsulant. In some embodiments, other particles are mixed with theencapsulant, such as particles that adjust the index of refraction ofthe encapsulant or other properties of the encapsulant.

Bond pads (not shown) may be formed on the top surface of the mount, tofacilitate electrical connection between UVLED 1 and another structure.Bond pads must be electrically connected to pads 42. If reflective layer44 is conductive (such as, for example, aluminum), bond pads may beformed on reflective layer 44. In some embodiments, the reflective layer44 may be formed over the bond pads, then removed by, for example,etching or any other suitable technique, to expose the bond pads.

In each of FIGS. 1, 4, 5, 8, 9, and 10, the UVLED 1 attached to themount may be a commercially available UVA, UVB, and UVC LEDs in thevarious embodiments. FIGS. 2 and 3 illustrate a portion of one exampleof the assignee's own UVB and UVC LEDs, which may be used in embodimentsof the invention. FIG. 2 is a top down view of a portion of a UVLEDcomposed of an array of UVLED pixels 12. FIG. 3 is a bisectedcross-section of a single UVLED pixel 12. Any suitable UVLED may be usedand embodiments of the invention are not limited to the structuresillustrated in FIGS. 2 and 3.

The UVLEDs are typically III-nitride, and commonly GaN, AlGaN, andInGaN. The array of UV emitting pixels 12 is formed on a singlesubstrate 14, such as a transparent sapphire substrate. Other substratesare possible. Although the example shows the pixels 12 being round, theymay have any shape, such as square. The light escapes through thetransparent substrate, as shown in FIG. 3. The pixels 12 may each beflip-chips, where the anode and cathode electrodes face the mount.

Semiconductor layers are epitaxially grown over the substrate 14. (Thedevice may include one or more semiconductor layers, such as conductiveoxides such as indium tin oxide, that are not epitaxially grown, but aredeposited or otherwise formed.) An AlN or other suitable buffer layer(not shown) is grown, followed by an n-type region 16. The n-type region16 may include multiple layers of different compositions, dopantconcentrations, and thicknesses. The n-type region 16 may include atleast one Al_(a)Ga_(1-a)N film doped n-type with Si, Ge and/or othersuitable n-type dopants. The n-type region 16 may have a thickness fromabout 100 nm to about 10 microns and is grown directly on the bufferlayer(s). The doping level of Si in the n-type region 16 may range from1×10¹⁶ cm⁻³ to 1×10²¹ cm⁻³. Depending on the intended emissionwavelength, the AlN mole fraction “a” in the formula may vary from 0%for devices emitting at 360 nm to 100% for devices designed to emit at200 nm.

An active region 18 is grown over the n-type region 16. The activeregion 18 may include either a single quantum well or multiple quantumwells (MQWs) separated by barrier layers. The quantum well and barrierlayers contain Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N, wherein 0<x<y<1, xrepresents the AlN mole fraction of a quantum well layer, and yrepresents the AlN mole fraction of a barrier layer. The peak wavelengthemitted by a UV LED is generally dependent upon the relative content ofAl in the AlGaN quantum well active layer.

A p-type region 22 is grown over the active region 18. Like the n-typeregion 16, the p-type region 22 may include multiple layers of differentcompositions, dopant concentrations, and thicknesses. The p-type region22 includes one or more p-type doped (e.g. Mg-doped) AlGaN layers. TheAlN mole fraction can range from 0 to 100%, and the thickness of thislayer or multilayer can range from about 2 nm to about 100 nm (singlelayer) or to about 500 nm (multilayer). A multilayer used in this regioncan improve lateral conductivity. The Mg doping level may vary from1×10¹⁶ cm⁻³ to 1×10²¹ cm⁻³. A Mg-doped GaN contact layer may be grownlast in the p-type region 22.

All or some of the semiconductor layers described above may be grownunder excess Ga conditions, as described in more detail in US2014/0103289, which is incorporated herein by reference.

The semiconductor structure 15 is etched to form trenches between thepixels 12 that reveal a surface of the n-type region 16. The sidewalls12 a of the pixels 12 may be vertical or sloped with an acute angle 12 brelative to a normal to a major surface of the growth substrate. Theheight 138 of each pixel 12 may be between 0.1-5 microns. The widths 131and 139 at the bottom and top of each pixel 12 may be at least 5 micronsin some embodiments and no more than 200 microns in some embodiments.Other dimensions may also be used.

Before or after etching the semiconductor structure 15 to form thetrenches, a metal p-contact 24 is deposited and patterned on the top ofeach pixel 12. The p-contact 24 may include one or more metal layersthat form an ohmic contact, and one or more metal layers that form areflector. One example of a suitable p-contact 24 includes a Ni/Ag/Timulti-layer contact.

An n-contact 28 is deposited and patterned, such that n-contact 28 isdisposed on the substantially flat surface of the n-type region 16between the pixels 12. The n-contact 28 may include a single or multiplemetal layers. The n-contact 28 may include, for example, an ohmicn-contact 130 in direct contact with the n-type region 16, and ann-trace metal layer 132 formed over the ohmic n-contact 130. The ohmicn-contact 130 may be, for example, a V/Al/Ti multi-layer contact. Then-trace metal 132 may be, for example, a Ti/Au/Ti multi-layer contact.

The n-contact 28 and the p-contact 24 are electrically isolated by adielectric layer 134. Dielectric layer 134 may be any suitable materialsuch as, for example, one or more oxides of silicon, and/or one or morenitrides of silicon, formed by any suitable method. Dielectric layer 134covers n-contact 28. Openings formed in dielectric layer 134 exposep-contact 24.

A p-trace metal 136 is formed over the top surface of the device, andsubstantially conformally covers the entire top surface. The p-tracemetal 136 electrically connects to the p-contact 24 in the openingsformed in dielectric layer 134. The p-trace metal 136 is electricallyisolated from n-contact 28 by dielectric layer 134.

FIG. 2 is a top view of four of the pixels illustrated in FIG. 3. Thep-trace metal 36, which covers the entire surface, is omitted forclarity. The p-contact 24 is smaller than and substantially concentricwith the edge 26 of the mesa that forms each pixel 12. The n-contact 28is disposed in the region between the pixels 12. Except for openings inthe n-contact 28 to accommodate the pixels, the n-contact 28 forms acontinuous sheet, which extends to the edge of the device into n-contactpad (not shown). The n-contact 28 and p-contact 24 are electricallyisolated by dielectric layer 134, which extends over the sidewalls ofeach pixel, as illustrated in FIG. 3.

Robust metal pads electrically connected to the p-trace metal 136 andn-contact 28 are provided outside of the drawing for connection to themount. Multiple pixels 12 are included in a single UVLED. The pixels areelectrically connected by large area p-trace metal 136 and the largearea n-trace metal 132. The number of pixels may be selected based onthe application and/or desired radiation output. A single UVLED, whichincludes multiple pixels, is illustrated in the following figures asUVLED 1.

In some embodiments, substrate 14 is sapphire. Substrate 14 may be, forexample, on the order of a hundred of microns thick. Substrate 14 mayremain part of the device in some embodiments, and may be removed fromthe semiconductor structure in some embodiments.

The UVLED may be square, rectangular, or any other suitable shape whenviewed from the top surface of substrate 14, when the device is flippedrelative to the orientation illustrated in FIG. 3. The length of theUVLED may be, for example, at least 150 μm in some embodiments, and nomore than 1 mm in some embodiments.

FIG. 1 illustrates a device with an encapsulant with a shaped sidewall.A device such as the device illustrated in FIG. 1 exhibited increasedoptical gain, as compared to a device where the sidewall of theencapsulant is not shaped. In some embodiments, the closer the shapedsidewall is to the UVLED 1, the larger the optical gain observed fromthe shaped sidewall. The spacing 45 between an edge of the UVLED 1 andthe shaped sidewall may be, for example, at least 0 mm in someembodiments, no more than 1 mm in some embodiments, at least 0.1 mm insome embodiments, no more than 0.5 mm in some embodiments, and at least0.2 mm in some embodiments.

In the device of FIG. 4, a reflective material 50 is disposed adjacentand outside the encapsulant 46. The reflective material 50 may surroundthe encapsulant 46. The reflective material 50 may be, for example, anyof the materials described above in the description of reflective layer44. The reflective material may be substantially the same thickness asencapsulant 46 in some embodiments, though in various embodiments thetop surface of reflective material 50 may be at the same level as thetop surface of encapsulant 46, higher than encapsulant 46, or lower thanencapsulant 46 (as illustrated in FIG. 4). In some embodiments,circuitry or other structures that may be absorbing to the radiativepower emitted by UVLED 1, such as an electrostatic discharge protectionchip, are disposed outside the encapsulant 46, for example under thereflective material 50.

In the device of FIG. 5, features are formed in the top surface of theencapsulant 46. The features may be, for example, one or more trenches52 formed in the top surface of the encapsulant 46. FIG. 6 is a top viewof the device of FIG. 5. A trench 52 surrounds UVLED 1. The trench 52includes four segments that connect and make a square. The trenchillustrated in FIG. 5 has angled, straight sidewalls that meet at apoint at the bottom of the trench, though this is not required. Thesidewalls may be vertical or curved, and the sidewalls need not meet ina point. Other arrangements besides a square that surrounds the UVLED 1may be used, such as segments that are not connected, segments that arenot parallel to an edge of the UVLED 1, segments that are oriented indirections other than the directions shown, or any other suitablearrangement.

Other features besides trenches may be used, such as, for example, holesformed in the top surface, structures formed on the top surface, or anyother suitable feature. Holes may be formed, for example, in a line, inan array, or in a random pattern. Holes may be formed in one or moreregions on the top surface. A region without holes may separatedifferent regions with holes, and/or surround one or more regions withholes.

In some embodiments, the features are created by roughening of the topsurface, for example randomly or by patterning. Like the holes describedabove, a rough area may be formed in a line, or in a two dimensionalregion. A region without roughening may separate different regions withroughening, and/or surround one or more regions with roughening.

The features may extend from the top surface downward. The depth 58 ofthe features 52 may be at least 20% of the thickness 56 of theencapsulant in some embodiments, no more than 80% of the thickness insome embodiments, at least 40% of the thickness in some embodiments, andno more than 60% of the thickness in some embodiments.

In some embodiments, different types of features may be combined. Invarious embodiments, for example, the trench illustrated in FIGS. 5 and6 may be combined with, for example, roughening and/or holes formed in adifferent area of the top surface; a top surface may be formed withholes and roughening in the same or different areas; and any of theabove-described combinations may include regions of the top surfacewithout any features.

In the device of FIGS. 5 and 6, the features 52 are disposed in theencapsulant 46 away from UVLED 1. In the device illustrated in FIG. 7,features 60, which may be features such as the features illustrated inFIGS. 5 and 6, holes, roughening, or any other type of featuresdescribed in the accompanying text, are formed over UVLED 1. Featuresformed over the UVLED 1 are not limited to the arrangement shown in FIG.7.

The angled sidewalls 48 and features 52, 60 may be formed by anysuitable technique, including cutting with a razor blade or pizzacutter, with or without guides, cutting with a hula hoe, sawing with anangled or otherwise shaped blade, casting, patterning to form areas ofweak adhesion of the encapsulant, using a breaker with the desiredprofile or by tilting the structure to get a cut at the desired angle,laser cutting, stamping, molding, abrading, cutting, using tape or anair brush to remove portions of the encapsulant. In some embodiments,the angled sidewalls 48 and/or the features 52, 60 are formed within alayer of encapsulant, rather than by removing or shaping theencapsulant. For example, multiple silicones with different indices ofrefraction may be used to form feature 52. The encapsulant 46 may be onesilicone, and the feature 52, rather than being filled with ambient gas,may be filled with a second silicone with a different index ofrefraction. Many of the above described techniques for forming angledsidewalls and features may be automated.

In some embodiments, grooves are formed on the sidewalls 48 of theencapsulant 46, as illustrated in FIG. 11, which is a photograph of aportion of a sidewall 48 disposed over a mount 40. Reflector 44 isvisible. LED 1 is disposed beneath the encapsulant 46 and not visible.As illustrated in FIG. 11, substantially vertical ripples or grooves maybe formed on the surface of the sidewall 48, such that the sidewall iscorrugated. Ripples 80 may be introduced, or may be a by-product of aprocess used to formed an angled sidewall 48. For example, whenencapsulant 46 is silicone and angled sidewall 48 is cut with a blade,microscopic defects or debris on the blade may form the ripples 80. Theripples may be, for example, on the order of a few microns wide, andspaced on the order of a few microns apart. The ripples or corrugationneed not be vertical, it may be angled relative to a major surface ofthe mount 40. Features formed in a top surface of the encapsulant mayalso have rippled or corrugated sidewalls, such as the rippled sidewallillustrated in FIG. 11.

FIG. 8 illustrates a device where a reflector cup 64 with reflectivesidewalls is formed in the mount, and the UVLED 1 is disposed at thebottom of the reflector cup. As an alternative, rather than a reflectorcup that extends down from the top surface of mount, a pedestal thatextends upward from the top surface of the mount may be formed, and theUVLED 1 may be disposed on the pedestal.

FIG. 9 illustrates a device where the UVLED 1 is disposed within aparabolic reflector 68 with reflective sidewalls. A UVLED 1 covered by ashaped encapsulant 46 is disposed at the center of the parabolicreflector. The parabolic reflector 68 may be any suitable structure suchas machined aluminum, Teflon, stainless steel, or a non-reflectivematerial coated with any suitable reflective material. The parabolicreflector 68 may be, for example, a hollow structure that is bolted,glued, or otherwise attached to the mount 40. In some embodiments,rather than having a shaped sidewall 48 as illustrated, the encapsulantmay fill the entire bottom of the parabolic reflector 68, and features52 and/or 60 may be formed in the top surface of the encapsulant.

In some embodiments, one or more chips containing circuitry such as, forexample, an electrostatic discharge protection chip may be attached tothe mount and electrically connected to the LED 1. Such a chip may bedisposed under the encapsulant 46 or outside encapsulant 46, underreflective material 50 in FIG. 4, outside reflector 68 as illustrated inFIG. 9 (chip 82), or in any other suitable position.

FIG. 10 illustrates a device where the encapsulant 70 over the UVLED 1has regions with different indices of refraction. In some embodiments,the portion 74 of the encapsulant 70 close to the mount 40 has a higherindex of refraction than the portion 72 of the encapsulant 70 furthestfrom the mount. In some embodiments, the index of refraction in theencapsulant 70 is graded across the thickness of the encapsulant, from ahighest value nearest the mount, to a lowest value furthest from themount. In some embodiments, the encapsulant 70 is silicone or othersuitable material mixed with bubbles of air or other gases. As theencapsulant is dispensed or otherwise disposed over the UVLED 1, the airbubbles rise to the top. The encapsulant closest to the mount has thelowest concentration of air bubbles, and therefore the highest index ofrefraction. The encapsulant furthest from the mount has the highestconcentration of air bubbles, and therefore the lowest index ofrefraction. In some embodiments, the encapsulant is silicone or othersuitable material mixed with beads, such as quartz beads. Since thequartz beads sink rather than rise, the mount and UVLED 1 may beinverted onto a quantity of encapsulant mixed with beads, such that thehighest concentration of beads (and the lowest index of refraction) isfurthest from the mount 40, and the lowest concentration of beads (andthe highest index of refraction) is closest to the mount.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit of the inventiveconcept described herein. In particular, different features andcomponents of the different examples described herein may be used in anyof the other examples, or features and components may be omitted fromany of the examples. A characteristic of a structure described in thecontext of one embodiment, may be applicable to any embodiment.Therefore, it is not intended that the scope of the invention be limitedto the specific embodiments illustrated and described.

What is being claimed is:
 1. A device comprising: an ultra-violet lightemitting diode (UVLED) comprising a semiconductor structure comprisingan active layer disposed between an n-type region and a p-type region,wherein the active layer emits UV radiation; a mount, wherein the UVLEDis disposed on a top surface of the mount; and an encapsulant disposedover the UVLED, the encapsulant having a top surface and substantiallyflat sidewalls that have a roughened surface, the roughened surfacecomprising grooves in the sidewalls substantially perpendicular to thetop surface of the mount.
 2. The device of claim 1 wherein the roughenedsurface comprises a corrugated surface.
 3. The device of claim 1 whereinthe roughened surface comprises ripples.
 4. The device of claim 1wherein the sidewalls are sloped.
 5. The device of claim 4 wherein thesidewalls slope outward from the top surface of the mount to the topsurface of the encapsulant.
 6. The device of claim 4 wherein thesidewalls slope inward from the top surface of the encapsulant to thetop surface of the mount.
 7. The device of claim 1 wherein the topsurface of the encapsulant is also a roughened surface.
 8. The device ofclaim 1 wherein the roughened surface comprises the grooves directlyformed in the sidewalls of the encapsulant by removing portions of theencapsulant.
 9. The device of claim 1 wherein an index of refraction ofthe encapsulant varies across a thickness of the encapsulant.
 10. Thedevice of claim 1 wherein the encapsulant has a square shape.
 11. Thedevice of claim 10 further comprising a trench formed in a top surfaceof the encapsulant, the trench having a square shape that surrounds theUVLED.
 12. The device of claim 10 further comprising a trench formed ina top surface of the encapsulant, the trench having a cross shape. 13.The device of claim 1 wherein the encapsulant comprises a transparentmaterial mixed with one of bubbles and beads.
 14. The device of claim 1wherein a plurality of holes are formed in the encapsulant.
 15. Thedevice of claim 1 wherein the encapsulant is pre-formed then mountedover the UVLED.
 16. The device of claim 1 wherein the encapsulant isdeposited as a liquid or semi-solid over the UVLED and shaped.
 17. Thedevice of claim 1 wherein the sidewalls are sloped at a constant angle.